Current duplicators (also known as current copiers) are used in today's high accuracy digital-to-analog converters (DACs) to generate an output current from a reference current, i.e., calibration current, more accurately than conventional current mirror technology. The main component of a current duplicator, a transconductor having a transconductance, gm, can also be used as a component of a sample and hold circuit in high accuracy analog-to digital-converters (ADCs). (High accuracy DACs and ADCs are devices operating on data segments greater than 8 bits in size.)
A current duplicator receives a difference current, converts the difference current into a voltage, stores the voltage and converts the stored voltage into an output current which is supplied to a load during a supply time period. During a calibration time period, the duplicator is disconnected from the load and any of the stored voltage dissipated during the supply period is replenished with reference to the calibration current. That is, the current duplicator is calibrated. The ultimate goal is to have the output current supplied to the load during the supply period equal the calibration current. The closer the output current is to the calibration current, the more accurate the current duplicator is.
The calibration period of a current duplicator used in existing DACs is inversely proportional to its accuracy. That is, for an increase in accuracy, there is a decrease in speed (a longer calibration period is required), and an increase in speed forces a decrease in accuracy. Therefore, when selecting a high accuracy DAC using current duplicator technology, one is forced to compromise speed for accuracy and vice versa.
Likewise, the sampling period of a sample and hold circuit used in existing ADCs is inversely proportional to its accuracy.